The objectives of the originally proposed research were two-fold: (1) to learn more fundamentally about the stages of altered function that lead to full activation of macrophages and the expression of cytolytic activity for neoplastic cells, and (2) to determine how this process is subverted in progressively growing neoplasms. The progress of our research has been halted by what appears to be subclinical infection in our mice. The problem manifests itself as partial or full activation of macrophages, resulting in spontaneous tumor cell killing by freshly explanted resident peritoneal macrophages, hyperresponsiveness to lipopolysaccharide or lymphokine, and a variety of other aberrations. We propose to resolve this problem, having tried to do so unsuccessfully using other approaches, by breeding and maintaining our own specific pathogen-free mice. The colony on our campus from which these mice will be derived has provided animals whose macrophages responded normally in pilot studies alongside macrophages derived from conventional mice that behaved abnormally. A breeding nucleus will be maintained in the SPF colony; however, due to space considerations, mice for production breeding and experimental use will have to be kept in conventional facilities. This application is for funds to provide laminar flow cage racks, a part-time animal caretaker and the increased per diem allowance that will be needed to maintain production breeders and mice for experimental use in specific pathogen-free, restricted-access, conventional quarters.